Refer to the previous exercise and the solution to (b).

a. The sample proportion of malformations is much higher in the highest alcohol category than the others because, although it has only one malformation, its sample size is only 38. Is the result sensitive to this single malformation observation? Re-fit the model without it (using 0 malformations in 37 observations at that level), and re-evaluate estimated probabilities of malformation at alcohol levels 0 and 7 and the relative risk.

b. Is the result sensitive to the choice of scores? Re-fit the model using scores

(0, 1, 2, 3, 4), and re-evaluate estimated probabilities of malformation at the lowest and highest alcohol levels and the relative risk.

c. Fit a logistic regression or probit model. Report the prediction equation.

Interpret the sign of the estimated effect.